With tens or an even larger number of antennas utilized, large-MIMO systems have many potential merits. However, there are also some difficulties with its practical realization. For example, the feedback overhead caused by sending back a large precoding matrix is heavy. In this paper, we propose a selective linear transceiver scheme to reduce the overwhelming feedback overhead in correlated large-MIMO systems. In line with the required reduced amount of feedback, antennas which can provide a potentially large diversity gain are firstly chosen independently of the actual channel realization. The transceiver is then designed over correlated MIMO channels in an iterative way to minimize the sum of detection errors under the transmit power constraint. Although optimal solutions for the case of full transceiver have been given under some special scenarios, we modify them to improve the BER performance of systems. Monte-Carlo simulation results verify that the proposed selective linear transceiver is a useful scheme in large-MIMO systems to provide a tradeoff between performance and feedback overhead.
This paper mainly deals with the problem of detecting a target against spherically invariant random vector (SIRV) clutter in the presence of steering vector mismatches. Assuming that the mismatch of the steering vector satisfies the conic constraint, the generalized likelihood ratio test (GLRT) is devised, and the geometry description is proposed for the derived solution. Additionally, the fully adaptive GLRT is derived by replacing the exact covariance with fixed point estimate (FPE). Finally, several numerical results are provided and discussed.
The miniaturized dual-mode dual-band band-pass filters (BPF) using Minkowski-island-based (MIB) fractal patch resonators are proposed in this paper. The BPF is mainly formed by a square patch resonator in which a MIB fractal configuration with 2nd order iteration is embedded in the patch. By perturbation and inter-digital coupling, the wide-band and dual-band responses are obtained respectively. For miniaturized wide-band design, at 2.41 GHz central frequency it has good measured characteristics including the wide bandwidth of 2.26-2.56 GHz (3-dB fractional bandwidth of 12.4%), low insertion loss of 0.72 dB, high rejection level (-52.5/-44.9 dB), and a patch size reduction with 60.6%. For compact dual-band design, the proposed filter covers the required bandwidths for WLAN bands (2.20-2.96 GHz and 4.74-5.85 GHz). The patch size reduction of 78.1% is obtained. Two transmission zeros are placed between the two pass-bands and resulted in good isolation.
Terahertz spectroscopy is a new tool for real time biological analysis. Unfortunately, investigations on aqueous solutions remain difficult and need to work on nanovolumes. Integrated Terahertz instrumentation remains a challenge. We demonstrate that Planar Goubau Line (PGL) technology could bring a real practical solution to reach this goal. This study provides the design, fabrication and test results of passive PGL components like loads and power divider. These PGL components are designed, simulated, fabricated and measured with a Vectorial network analyser (VNA). Simulation and test data support PGL component designs. PGL components operate over a wide frequency range from 0.06 to 0.325 THz.
A novel circularly polarized antenna with a circular radiating aperture and circular ground plane for broadband characteristics is presented in this paper. The vertical and horizontal components of the L-shaped probe are separated and placed at the front and back sides of the substrate. The antenna is excited by a microstrip line which is connected to the vertical component of the L-shaped probe and electromagnetically couples the signal to the horizontal component of the L-shaped probe. The concept of placing an appropriate stub in the slot, by observing the electric field vector behaviour in the slot, is proposed to enhance the axial ratio (AR) bandwidth by around 15%. The fabricated antenna shows wideband impedance and circular polarization characteristics of 48% along with a maximum gain of 6 dBic. The measured and simulated antenna characteristics are in good agreement.
In this paper, a deterministic strategy to generate the aperiodicity, based on three geometric taper distributions is studied and validated. The method is applied to study arrays with average inter-elements spacing larger than a wavelength, exhibiting a reduction of the grating lobe level and requiring lower aperture size against a periodic structure with same directivity. Finally, a microstrip patch aperiodic array has been designed, manufactured and measured for an experimental validation of the concept, obtaining good agreement between simulated and measured radiation patterns. This manufactured antenna demonstrates experimentally the reduction of the grating lobes with a similar level to the side lobe.
In this paper, a rectifying antenna (rectenna) for energy scavenging applications is presented. The proposed device uses a modified bowtie antenna to collect the electromagnetic energy coming from UHF RFID systems, and RF Schottky diodes to convert it into DC power. Experimental results at 866 MHz demonstrating an RF-to-DC conversion efficiency of about 65% with an input power density of 60 μW/cm2 will be presented and discussed.
The design of a 2n×2n Butler matrix is usually based on an iterative process. In this paper, recurrence relations behind this process are found, and the close-form solutions, i.e., non-recursive functions of n, are reported. These solutions allow the direct derivation of the scattering matrix coecients of symmetric and large Butler matrices.
In this paper, we have analyzed the channel capacity by using the maximal-ratio combing (MRC) diversity scheme for communication systems operating over a composite fading environment modeled by the Generalized-K distribution at the receiver. For the Generalized-K fading channel with arbitrary values for small and large scale fading parameters, we have derived a closed-form expression for the moment generating function (MGF) of the received signal-to-noise ratio (SNR) and utilized it to obtain a novel closed-form expressions for the channel capacity under different adaptive transmission schemes. The result of the proposed methods is compared with other reported literature to support the analysis.
In this paper, a new configuration of Tapered Slot Antenna (TSA) with improved radiation pattern is proposed and studied. This antenna is designed in the form of a substrate integrated waveguide (SIW) array with respect to side lobe level constraints. For side lobe reduction, a simple quasi-triangular distribution is proposed and is accomplished uniquely by means of 3 dB power dividers. A 12-way series feed network with T-junction is designed and demonstrated. Radiation features of the antenna array are discussed to illustrate the accomplishment of a low side lobe level (-19 dB) of the array. The proposed antenna demonstrates the ability of the SIW technology to achieve a very low side lobe in a simple, compact and planar structure.
A wideband slotted multifunctional reconfigurable antenna is proposed for WLAN/WiMAX/UWB/PCS-DCS/UMTS applications. The proposed antenna consists of monopole and spiral sections and microstrip feeding. A microstrip patch on FR4 substrate provides wideband return loss for each application. Total area of the antenna is 34×45 mm2 that satisfies all the requirements for different applications in a low profile structure. Reconfigurable design is used in this antenna using RF MEMS switches. The proposed antenna has a nearly omnidirectional radiation patterns (doughnut shape) in different frequency bands. The notch is embedded in the ground plane to improve the impedance matching, and the dimensions of this notch are optimized. Moreover, the variation of group delay is about ±2 ns in UWB application. Also a prototype of the proposed antenna is fabricated, and the results are compared with those obtained from simulations. Measured return losses are in good agreement with simulated ones. The proposed antenna has the advantages of multifunctional operation, low profile, low cost and omnidirectional pattern.
This paper introduces a new design technique for a capacitive gap-coupled bandpass filter (BPF) using non-uniform arbitrary image impedances. Based on the proposed BPF equivalent circuit model, the filter's design equations are derived, and they are validated from comparisons of the calculated and simulated results. For this theoretical verification, the BPF using non-uniform arbitrary image impedances is designed using the specifications of: center frequency (fc)=5.8 GHz, fractional bandwidth (FBW)=3.5%, and filter stage (N)=3. The calculated and simulated results of the designed filter show good agreement. The BPF using the proposed design method could provide an advantage that one can arbitrarily determine two different image impedances, which ultimately affects the BPF's coupling gaps and line widths. This could result in suitable filter dimensions, i.e., gaps and line width, for a conventional low resolution photolithography fabrication although a low or high dielectric constant substrate is used for the design.
Ultra wideband components have been developed using SIW technology. The various newly developed components include a GCPW transition, Y and T-junctions. The GCPW transition covers over 10 GHz bandwidth with less than 0.4 dB insertion loss. The optimized T and Y-junctions have relatively wide bandwidths of greater than 40% that have less than 0.6\,dB insertion loss. The developed transition was utilized to design an X-band eight-way power divider that demonstrated excellent performance over a 4 GHz bandwidth with less than ±4º and ±0.9 dB phase and amplitude imbalance, respectively. Theoretical and experimental results are presented and compared with previously designed SIW power dividers. The developed SIW power divider has a low profile and is particularly suitable for circuits' integration.
A novel coplanar waveguide (CPW)-fed circularly polarized (CP) antenna is proposed. The antenna is composed of a square ground plane with a circular slot and an equiangular tapered-shaped feedline. With the use of a special shaped feedline, the axial ratio (AR) bandwidth of the proposed antenna is about 61.9% (2.9-5.5 GHz), which is larger than most of similar antennas proposed before. In addition, the impedance bandwidth, determined by 10-dB return loss, is between 2.9-20 GHz, which makes the antenna be used for ultra-wideband (UWB) applications.
In this paper, a calibration technique for the position sensor via support vector regression (SVR) is proposed. The position sensor adopts a zero-intermediate frequency architecture based on a six-port network, which is used for directly measuring the phase differences and indirectly reflecting the position. The SVR, which implements the structural risk minimization (SRM) principle, provides a good generalization ability from size-limited data sets. The results indicate that the SVR model can achieve a great predictive ability in positioning, with an accuracy of 2.41 mm over a distance range of 274.5 mm.
We investigate experimentally the collisions of nonlinear envelope pulses in a left-handed transmission line with regularly spaced Schottky varactors. By measuring the test line, we successfully observed that when two nonlinear envelope pulses traveling in opposite directions collide, two new envelope pulses are developed. These new pulses satisfy the phase-matching condition, and their carrier wave frequencies are the sum of the carrier wave frequencies of the original pulses. This article describes the experimental observations, together with the fundamental properties and numerical performance prospects of the test line.
The development of a compact metal mountable Radio-Frequency IDentification (RFID) tag antenna on a ceramic substrate based on Barium Titanate is presented. The performance limitations and design trade-offs of metal mountable RFID tag antennas are reviewed and the favorable features of a high-permittivity antenna substrate for the development of antennas for metal mountable RFID tags are discussed. The simulation-based tag antenna design process is outlined and the measured read range of the developed metal mountable tag on conductive platforms of various sizes is presented.
A tunable impedance matching network is applied to achieve very widely tunable antennas, whose geometries are independent and unchanged to simplify the design. The attached matching network as the antenna feeding network enables any unspecified UWB antenna to tune the operation frequency continuously with high selectivity by merely one single control. This is quite different from filter-based concept which is complicated to co-design and implement a tiny narrow band tunable filter over wide frequency ranges and very difficult to control with one element. And also the design, adjustment, and optimization of the matching network are much simpler, quicker, and lower cost than geometry-modified antenna design. The analysis of precise high frequency circuit models is used predict the performance in simulation. Fabricated prototype antennas are measured by using horn antennas to validate the antenna performance. The tunable frequency ranges from 1.8 GHz to 2.8 GHz (155%) and 2.19 GHz to 3.86 GHz (176%). Moreover, compared to other matching network-based solutions, non-ideal effects in undesired bands other than the operation frequency band are suppressed, so the performance is improved. One wide-tuning antenna using one single element to control can be carried out by tunable matching networks without complicated designs.
This paper proposes a compact ultrawideband monopole antenna fed by CPW with a 5.5 GHz notched band of WLAN/WiMAX systems. The antenna input section is designed by using a gradual curvature central line and ground planes for ultrawideband achievement. In order to reject the unwanted frequency of the existing WLAN/WiMAX band, the C-shaped slit with perimeter length of a half wavelength at center frequency of 5.5 GHz has been embedded into the monopole patch. The designed antenna is completely implemented and measured for impedance bandwidth covering UWB range and stably performs omnidirectional pattern in $xz$ plane from 3.1 to 10 GHz. The proposed antenna could potentially minimize frequency interference in the WLAN/WiMAX bands.
A unilateral circuit model, which precisely predicts small signal response over a wide range of frequencies and bias points, is quantitatively analyzed and presented. The shortfall of current unilateral assumption and transformation technique is presented. A complete and explicit analysis is provided to develop a compact unilateral circuit model. The model is intended to predict input reflection, forward transmission and output reflection coefficients over wide range of frequencies. The technique is validated by transforming bilateral a small signal model of 3 x 3 μm x 40 μm, InGaP/GaAs HBT into its unilateral equivalent over the frequency range of 250 MHz to 30 GHz. The accuracy of the technique is corroborated at various bias conditions; collector current from 3 mA to 150 mA and collector-emitter voltage from 1 V to 5 V. Simulated results show very good agreement between small signal responses of transformed unilateral and bilateral circuit models.